There are many ways to deliver digital video signals to a subscriber. For example, compressed digital video using the motion picture experts' group (MPEG-2) compression/decompression methodology can be delivered using a variety of media including coaxial cable, fiber optic cable and satellite. Some of these delivery systems are considered "video-on-demand," or "near video-on-demand" in that a user, or subscriber, may select from a plurality of offerings and view a particular program as desired from time to time. In video-on-demand systems a user may select a program for viewing at any arbitrary time. In near video-on-demand systems, a user is typically given a choice of programming available at repeated specific times. Furthermore, broadcast video applies to programming that occurs with a daily or weekly schedule and is delivered to a wide number of subscribers at the same time.
The video programming can be delivered to a receiver via a number of methodologies, for example but not limited to, satellite, cable, fiber optic technology, etc. After receipt of the programming source content, these systems can use coaxial or fiber optic cabling technology to deliver the video programming received by a digital receiver to the MPEG-2 digital video broadcast (DVB) equipment using the DVB-ASI communication standard. DVB-ASI is a communication standard based on MPEG-2 that specifies the manner in which MPEG-2 data are transmitted via coaxial or fiber optic cabling.
The DVB-ASI interface uses what is referred to as an 8 bit to 10 bit (8B/10B) encoding scheme in which each byte (8 bits) of data is encoded into a 10-bit data word. There are 2.sup.8 (256) possible characters that can be represented with 8 bits and there are 2.sup.10 (1024) possible characters that can be represented with 10 bits. In this manner an 8B/10B encoder utilizes a specially chosen 256-member subset of the 1024 possible characters to represent each 8-bit data byte. Such a system is described in U.S. Pat. No. 4,486,739 to Franaszek et al., entitled "BYTE ORIENTED DC BALANCED (0,4) 8B/10B PARTITIONED BLOCK TRANSMISSION CODE," and issued on Dec. 4, 1984. This system defines special 10 bit characters to be utilized that have no direct current (DC) bias and which have frequent bit transitions, two characteristics that are desirable in a serial communications link such as DVB-ASI.
Because only 256 out of a possible 1024 characters are used to represent each byte of data in a DVB-ASI data stream, there are numerous code characters to spare. Such a system enables some of the 10 bit characters to be coded differently from those that are used to represent an 8-bit data byte in a DVB-ASI data stream. These special characters can be utilized to perform user-defined functionality, and a subset of these special characters, known as comma characters, enable a receiver to synchronize to the coded serial data stream. These special characters can also be used to communicate to the receiver that there were no data present in a particular byte in the data stream. The DVB-ASI protocol dictates that one of these comma characters, specifically the character designated K28.5, be periodically inserted into the data stream to allow a receiver the opportunity to synchronize to the input data stream.
The DVB-ASI standard allows up to approximately 213 Mbps data rate. It would be desirable to have a way in which to combine a number of these 8B/10B encoded DVB-ASI data streams into an aggregate higher speed 8B/10B encoded data stream for transport over a fiber connection. However, there must be some defined way of separating this higher speed 8B/10B encoded data stream back into its individual DVB-ASI components.
Therefore, there is a need in the industry for a manner in which to combine a number of 8B/10B encoded DVB-ASI data streams into an aggregate higher speed 8B/10B encoded data stream for transport over a fiber connection while allowing a receiving device to reliably synchronize to and separate the aggregate 8B/10B encoded data stream into the individual 8B/10B encoded DVB-ASI data streams.